An important event in atherogensis is the retention and aggregation of lipoproteins in the subendothelial space of both prelesional and lesional regions of the arterial tree. We discovered that sphingomyelinase (Smase) is a potent inducer of lipoprotein retention and aggregation in vitro and acts on LDL retained in animal and human lesions in vivo. Two other arterial wall molecules, namely, chonroitin sulfate proteogycans (CSPGs) and lipoprotein lipase (LpL), interact with Smase and promote these processes. The overall goal of this project is to expore the roles of arterial wall SMase, proteoglycans, LpL, and other specific arterial wall factors in subendothelial retention and aggregation of lipoproteins and atherogenesis. Regarding Smase, we recently found that cultured macrophages secrete a Smase that requires zinc (Zn-SMase) and that can hydrolyze LDL-SM under physiological conditions, especially inteh presence of LpL. Additional studies revealed, remarkably, that this Zn-SMase arises from the acid Smase (ASM) gene, which was known to give rise to lysosomal Smase (lys- SMase). Interestingly, others have postulated that deficiencies in lys- SMase might promote lesion pathology. With this background, the goals of Aim #1 are to determine if Zn-SMase arises from alternative splicing or from protein modification; to obtain antibody and nucleotide probes to determine the prsence and location of Zn-SMase in lesions; and to conduct lipoprotein retention and aggregation and atherosclerosis studies in available ASM knockout and planned Zn- SMase transgenic mice crossed with apo B and LpL transgenic mice. We also propose to detemrine if heterozygous deficiency of ASM affects atherosclerosis in humans. Finally, we will begin studie son another SMase, Mg-SMase, that we found is present in normal, Mphi- poor aorta and may therefore play a role in early atherogenesis at prelesional sites. In Aim #2, we will determine the roles of chondroitin-6 sulfation and specific core protein expression in lipoprotein retention and aggregation and atherogenesis. We will also study the relationship between LDL retention and arterial wall advanced glycosylation endproducts (AGEs). Last, we will examine possible variations in the retention and atherogenicity of lipoprotein(a) from whites and Asians ("high-risk") vs. Blacks ("low-risk"). The studies in this project fit well into the overall theme of the SCOR, namely, to use induced mutant mice and human genetic variations to investigate atherogenesis at the level of the arterial wall, and will involve extensive intereactions with Projects 2 (LpL), 3 (arterial HDL effects), and 4 (AGEs), and the Molecular Biology, Pathology, and Clinical Cores.